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The dynamic geometry of the left ventricle was assessed with the use of chronically implanted pulse-transit ultrasonic dimension transducers. The orientation of the transducers allowed the measurement of left ventricular minor and major axis diameters and equatorial wall thickness in the conscious dog. The left ventricle was modeled as a three-dimensional, prolate ellipsoidal shell. Left ventricular and pleural pressures were measured with high fidelity micromanometers. Aortic blood flow was obtained with electromagnetic flow probes. To test the assumptions inherent in this technique, left ventricular mass, internal volume, stroke volume, and peak aortic flow were computed from the dimension data and compared to directly measured values. Correlation coefficients of 0.95 or greater were obtained for each of these comparisons. In addition, the calculated left ventricular mass was constant to within +/- 6% of the mean value throughout the cardiac cycle. We found that the dynamic contraction pattern of the left ventricle was dependent on the physiological state of the dog. Furthermore, in the conscious state, shortening of the minor axis diameter, lengthening of the major axis diameter, and slight thickening or thinning of the wall were noted during isovolumic contraction (isovolumic ellipticalization pattern). In the open-chested, anesthetized state, however, marked rearrangements in geometry were observed during isovolumic contraction manifested by lengthening of the minor axis diameter, and significant thickening of the wall (isovolumic sphericalization pattern). We also observed that left ventricular volume was significantly diminished in the open-chested state. The isovolumic contraction pattern in open-chested dogs could be changed from sphericalization to ellipticalization by increasing end-diastolic volume with the infusion of saline. During a vena caval occlusion in the conscious state, the contraction pattern changed from isovolumic ellipticalization to isovolumic sphericalization as the end-diastolic volume decreased. Thus, the exact pattern of left ventricular contraction was found to be a function of left ventricular volume.